<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <title>全景图</title>
    <style>
        body {
            margin: 0;
            overflow: hidden;
        }

        #canvas {
            background-color: antiquewhite;
        }
    </style>
</head>

<body>
<canvas id="canvas"></canvas>
<!-- 顶点着色器 -->
<script id="vertexShader" type="x-shader/x-vertex">
    attribute vec4 a_Position;
    attribute vec2 a_Pin;
    varying vec2 v_Pin;
    void main(){
      gl_Position=a_Position;
      v_Pin=a_Pin;
    }
  </script>
<!-- 片元着色器 -->
<script id="fragmentShader" type="x-shader/x-fragment">
    precision mediump float;
    uniform vec2 u_CanvasSize;
    uniform sampler2D u_Sampler;
    varying vec2 v_Pin;
    vec2 center=u_CanvasSize/2.0;
    float diagLen=length(center);
    float pi2=radians(360.0);

    float getAngle(vec2 v){
      float ang=atan(v.y,v.x);
      if(ang<0.0){
          ang+=pi2;
      }
      return ang;
    }

    void main(){
      vec2 p=gl_FragCoord.xy-center;
      float ang=getAngle(p);
      float x=ang/pi2;
      float len=length(p);
      float y=len/diagLen;
      vec4 color=texture2D(u_Sampler,vec2(x,y));
      if(p.x>0.0&&abs(p.y)<1.5){
        color=texture2D(u_Sampler,vec2(0,y));
      }
      gl_FragColor=color;
    }
  </script>
<script type="module">
  import { initShaders, parseColorStops } from "../jsm/Utils.js";
  import Poly from './jsm/Poly.js'

  const canvas = document.querySelector("#canvas");
  canvas.width = window.innerWidth;
  canvas.height = window.innerHeight;

  // 获取着色器文本
  const vsSource = document.querySelector("#vertexShader").innerText;
  const fsSource = document.querySelector("#fragmentShader").innerText;

  //三维画笔
  const gl = canvas.getContext("webgl");

  //初始化着色器
  initShaders(gl, vsSource, fsSource);

  //声明颜色 rgba
  gl.clearColor(0, 0, 0, 1);

  const source = new Float32Array([
    -1, 1, 0, 1,
    -1, -1, 0, 0,
    1, 1, 1, 1,
    1, -1, 1, 0
  ]);

  const rect = new Poly({
    gl,
    source,
    type: 'TRIANGLE_STRIP',
    attributes: {
      a_Position: {
        size: 2,
        index: 0
      },
      a_Pin: {
        size: 2,
        index: 2
      },
    },
    uniforms: {
      u_CanvasSize: {
        type: 'uniform2fv',
        value: [canvas.width, canvas.height]
      }
    }
  })

  const image = new Image()
  image.src = './images/room.jpg'
  image.onload = function () {
    rect.maps = {
      u_Sampler: { image },
    }
    rect.updateMaps()
    render()
  }

  //渲染
  function render() {
    gl.clear(gl.COLOR_BUFFER_BIT);
    rect.draw()
  }

</script>
</body>

</html>
